On Thu, Apr 10, 2003 at 12:39:25PM +0200, Cyrille Chepelov wrote:
> Le Thu, Apr 10, 2003, ? 10:40:47AM +0100, Hamish Marson a ?crit:
> > I'm not sure how your logic works out that a 64 bit reg is going to
> > be faster than a 32bit one. Or do you mean simply you're expecting a
> > speedu because there are MORE 64 bit registers tahn 32 bit
> > registers?
>
> Reg pressure is pretty bad on x86; and int is still 32 bit on x86-64
> (IIRC, long is 64 bit and of course any T* ). So yes, anything which
> plays with pointers will be larger on x86-64, but it's not an
> automatic doubling in size of everything. And mapping libraries twice
> also eats a good deal of memory. OTOH, 16 general-purpose 8,16,32 or
> 64-bit registers (not even counting a large SSE2 register file as
> well) should help gcc feel more at home (especially with less code
> dedicated to handling register<->memory swap-outs)
>
> I don't have numbers to back either choice, but it looks to me that a
> mixed userland with everything duplicated should be a last resort. And
> I'm sure some people have numbers out these.
Based on the numbers I've seen, the factors mentioned seem to balance
each other out fairly well. I'm not (yet) allowed to talk about the
details though ...
--
Colin Watson [cjwatson@flatline.org.uk]